I knew God was a Trotskyite. Cern's absurdly oversold answer to the who-is-God question was snuffed out in Switzerland last week by a celestial helium leak. Don't dabble with the big bang: the curse will get you.

Meanwhile, who-are-we questions are being answered as never before - and at a fraction of the cost. Archaeologists excavating at Stonehenge, for the first time in half a century, are rewriting the map of British prehistory. Once again it is our old friend, Preseli bluestone, that is hero of the hour. Its glories shall not go unsung.

Wainwright and Darvill might sound like a pair of Yorkshire undertakers, but the two professors have long been testing their thesis that the secret of this great monument lies in its most sensational feature: the inner circle of bluestones from the bleak Preseli mountains in Pembrokeshire. Most come from a specific 3km slope on Carn Menyn, Wales's answer to Athens' Pentelicon.

The myriad past theories of Stonehenge mostly take refuge in magic and religion. Inigo Jones cited the Roman gods, John Aubrey and William Stukeley the druids, while more recent aficionados proffer astronomy and even chronology, though who needed a clock on this scale is puzzling. The henge has also represented a serpent's egg, a vulva and a kingly shrine. Aliens, wizards and dragons have had their brief hour on its stage.

All these theories collapse before the bluestone question. Why go to the colossal effort and expense of moving four-tonne megaliths 250km (150 miles) across land and sea from Preseli, a work of global engineering comparable only with the contemporary building of the Great Pyramid at Giza? And why then surround them so reverentially with 25-tonne sarsens?

A suggested answer was given by Geoff Wainwright and Tim Darvill to the Society of Antiquaries two years ago, before the start of the current dig. They claimed that the bluestone - dark blue when freshly cut and speckled with white quartz - was thought to have curative properties. In other words, the key to Stonehenge lay not in magic or religion, but in the worldly human craving for longevity and pain relief. It was in the here and now, not the hereafter. As Darvill put it this week, Stonehenge was "the neolithic A&E unit for southern England".

Six years of excavation at Preseli have revealed settlements as old as four millennia BC, before Stonehenge. Burials also suggest visitors from far afield. The hills are peppered with holy wells, most of them spilling over pieces of the dolerite bluestone placed at their mouths, some carrying carved decoration. The stone, unique to the Preseli area, was clearly special.

To the old archaeology, special tended to mean sacred. But the constant search for "primitivist" reasons for prehistoric phenomena is questioned by Wainwright and Darvill. Why not offer workaday, rational answers? Holy wells throughout history were curative, usually associated with components such as chalk, sulphur or iron.

The plethora of wells at Preseli and the associated burial mounds appear to go back long before the bluestones arrived at Stonehenge, about 2300BC. This suggests that the wells and their bluestones were famed far and wide, a reputation repeated by the (albeit unreliable) Geoffrey of Monmouth in the middle ages.

Into the 19th century, visitors could buy hammers in Amesbury to chip bits off Stonehenge in honour of the old tradition of its healing power. This may explain why only the underground parts of many of the bluestones survive, and why chippings are found in graves across the country, including at Silbury. Bluestone, like a copper bracelet, was plainly long thought to be a health-giving token.

Everything about Stonehenge begins to fall in place with this theory. The crippled Amesbury archer and his son, who science tells us originated from the Alps and then Kent, join the mass of burials of mutilated visitors who appear to have travelled to Stonehenge over the centuries. Isotope analysis of the teeth enamel of the local "Boscombe bowmen" reveals time spent in the bluestone country of south Wales - perhaps in search of a "second opinion".

Stonehenge's reputation must have been Europe-wide, explaining its uniquely splendid architecture. Like Lourdes (and like Harley Street), ceremony and even a touch of confidence trickery were adjuncts of the healing game. Hence the great processional way up from the river, the guarding sarsens and the mumbo jumbo of solstice alignment.

Hence also the riches emerging from excavations two miles away at Durrington Walls by Sheffield University's Mike Parker Pearson. This is revealing a town of some 300 houses, not just a prehistoric Lourdes but "the largest neolithic settlement in northern Europe". Parker Pearson's theory is that this was a place of kingly burial, not incompatible with the Lourdes thesis.

Yet even this week's newspaper reports could not avoid reference to druids, cults, pilgrims and magical powers. We seem to seek in superstition the answers to questions which we cannot wait for science to solve - just as we attribute the big bang to God. We want to see in Stonehenge a place of druids, dragons, horrors and Wordsworth's "gigantic beings ranged in dread array ... And like a thousand gods, mysterious council hold".

Science is now unfurling the prehistory of Britain with all the tantalising excitement of an ancient map found in a dusty basement. That its answers are commonsensical rather than supernatural is surely a virtue. Radiocarbon dating has brought Stonehenge to life in a way that the old archaeology never could. It has dated the earliest settlement of the site to 7000BC, dated each phase of construction and located the birth of the Amesbury archer and other remains.

What it has yet to crack is the most intriguing conundrum of all. The will to survive may be sufficient explanation for the appeal of the bluestones. But even quack remedies often have some basis in mineral and botanical fact.

Medical science has found therapies in chalybeate and mud, in herbs, roots, vegetables and even human urine. Is it possible there is something in Preseli dolerite and rhyolite, when dowsed by good clean water, that does indeed do you good? Research shows the springs to be full of chloride and sulphur. But the goodness lies in the water, not just the stone. Were the lordly proprietors of Hospice Stonehenge sold a complete pup by those wily Welshmen who forgot to mention, please add water?

Jacquetta Hawkes remarked that each age gets the Stonehenge it deserves, or perhaps the one that best reflects its concerns. Ours is the age of hypochondria. But even hypochondriacs can be ill, and can be cured. Ancient Britons were no different, and truly built themselves a national health service to last.